Ozone Hole May Have Caused Australian Floods

NEW YORK -- A new scientific study suggests that the severe flooding that hit northern Australia earlier this year may have not been caused by rising global temperatures induced by greenhouse gases, but rather by the hole in the ozone layer.

Research published last week by scientists at Columbia University's School of Engineering and Applied Science, in conjunction with partners in Canada, purports to demonstrate how the massive hole in the ozone layer of the atmosphere high above Antarctica is altering rainfall patterns in the Southern Hemisphere. The study ran in Science magazine Friday.

The scientific team says its members ran computer simulations designed to predict how changes in precipitation would likely be affected by the ozone hole, which scientists already say pulls the southern jet stream closer to the South Pole and leads to a southerly shift in tropical moisture. They then compared what that modeling predicted to the actual observed changes in climate recorded in the southern half of the planet.

The two matched up very closely, providing strong evidence that the famous hole in the ozone layer has been "the dominant agent of atmospheric circulation changes in the Southern Hemisphere in the last half century," according to a summary of the research.

"In these regions, our models show that the precipitation response to the ozone hole is unaffected by atmosphere-ocean interactions, is largely independent of the physical parameterizations of any one model or the sea surface temperatures, and originates almost entirely from ozone depletion in the southern polar regions," the paper states.

The study only looks at changes during summer in the Southern Hemisphere, when the ozone hole is most apparent, and covers observed climate changes from 1979 to 2000. But the team is confident that its results show that the formation of the ozone hole causes higher than normal precipitation along a belt of the tropics just south of the equator, a zone roughly encompassing central and southern Brazil, southern Africa and Australia.

"Previous studies have shown that the ozone hole changes the high-latitude circulation patterns, such as a southward shift of westerly jet," said Sarah Kang, a postdoctoral research scientist at Columbia Engineering's Department of Applied Physics and Applied Mathematics. "What we show is that this southward shift of high-latitude circulation also affects the tropical circulation to shift southward, and induces rainfall changes there."

Have ozone impacts been credited to climate change?
Though the research showed an estimated 30 percent increase in rainfall in eastern Australia in both the modeling and observations, Kang cautioned that it did not show a definitive link between the ozone layer hole and the rains that wrecked Brisbane and other areas earlier this year. She said other factors, in particular the La Niña weather pattern, could have played a role in that devastation.

Nevertheless, the study could have huge implications for climate science.

Though some ozone-depleting substances are covered in international climate treaties due to the potent greenhouse gas effects they cause, the hole in the ozone layer is not covered by the most recent reporting of the Intergovernmental Panel on Climate Change (IPCC).

And ozone-depleting gases that don't lead to rising temperatures are ignored by the international system established to address climate change. Those are left to the Montreal Protocol, considered one of the most successful multilateral environmental agreements ever devised.

Already, there is vigorous scientific debate over whether some recent extreme weather events were caused either by global warming or by the periodic changes to southern Pacific Ocean temperatures known as El Niño and La Niña. Evidence that the ozone hole could be causing large flooding in the southern tropics has never been considered before in the larger global warming debate.

While Kang declined to opine on the implications for global climate change treaties, senior research scientist Lorenzo Polvani suggested in a release that the Columbia University and Canadian research findings should in fact be taken into consideration.

"While the ozone hole has been considered as a solved problem, we're now finding it has caused a great deal of the climate change that's been observed," Polvani said.